Wind turbine generator having an eddy current brake, wind turbine having such a generator, and associated methods

ABSTRACT

A wind turbine generator includes an outer housing, a drive shaft rotatably mounted within the outer housing, stator and rotor assemblies positioned within the outer housing and movable relative to each other, a heat exchanger, and a blower having a rotating plate for generating a fluid flow circuit within the generator for transporting heat from the stator and rotor assemblies to the heat exchanger. An eddy current brake having a rotating member is located within the outer housing and is positioned in the fluid flow circuit such that fluid moving in the flow circuit cools the first rotating member. The blower and the eddy current brake may be integrated, such as by having the rotating plate of the blower serve as the rotating member of the eddy current brake. A wind turbine having such a generator, as well as a method of operating a wind turbine generator is also disclosed.

TECHNICAL FIELD

The invention relates generally to wind turbines, and more particularly,to a wind turbine generator having an eddy current brake positionedwithin the generator, a wind turbine having such a wind turbinegenerator, and methods for operating a wind turbine having an eddycurrent brake within the generator of the wind turbine.

BACKGROUND

Wind turbines are used to produce electrical energy using a renewableresource and without combusting a fossil fuel. Generally, a wind turbineconverts kinetic energy from the wind into mechanical energy and thensubsequently converts the mechanical energy into electrical power. Ahorizontal-axis wind turbine includes a tower, a nacelle located at theapex of the tower, and a rotor that is supported in the nacelle. Therotor is coupled with a generator for converting the kinetic energy ofthe blades to electrical energy.

Wind turbines are massive machines having relatively large masses movingat relatively high rates of speed. For example, the rotor of a modernwind turbine may weigh in the range of 25-50 tons and have blade tipspeeds around 300 ft/s. Additionally, generator components, such as therotor assembly which typically carries heavy magnets or the like, haveconsiderable weight and are subject to relatively high rotationalspeeds. Thus, it may be important to incorporate within a wind turbinemeasures or systems configured to control these components, and morespecifically, for reducing the rotational speed of these componentsunder certain conditions.

Conventional wind turbine designs may provide a number of ways to reducethe speed of the rotor and generator of the wind turbine. For example,many modern wind turbines include blade pitch mechanisms that allow theblades to rotate about their longitudinal axis to affect the aerodynamicforces acting on the blades. The pitch mechanisms may be used to pitchthe blades, for example, out of the wind so as to slow the wind turbinerotor and generator. Thus, for example, when wind conditions become highor excessive, the blades may be pitched in order to reduce the liftforces acting on the blades, and thus reduce the speed of the rotor andthe generator operatively coupled thereto. In a further example, in agrid fault, the electrical load on the generator drops suddenly, therebycausing the generator speed and rotor speed to suddenly increase. Inthese over-speed conditions, the blades may again be pitched in a mannerthat reduces the rotor and generator speeds.

In addition to pitch mechanisms, wind turbines may also include otherbraking mechanisms configured to reduce the speed of the rotor orprevent the rotor from turning. In this regard, wind turbines mayinclude mechanical braking systems that rely on friction between twosurfaces (e.g., rotor disc and pads) to reduce or restrict the rotationof the rotor. For example, various drum and disc brake systems have beenused in various wind turbine arrangements to reduce the speed of therotor and/or to secure the rotor in a parked position.

These braking systems, however, are not without their drawbacks. In thisregard, pitch-based rotor braking may impose stresses in other windturbine components, such as the wind turbine tower or foundation, forexample. Additionally, friction-based rotor brakes require regularmaintenance and replacement parts, including disc and pad replacementthat are subject to wear and damage. Moreover, friction-based rotorbrakes are primarily effective once the rotational speed of the windturbine rotor has already been significantly reduced. Thus, these typesof brakes may not be particularly useful under certain high speedconditions where it is desired to reduce the speed of the rotor.

Accordingly, there is a need for a braking system that addresses theseand other shortcomings of existing wind turbine braking systems. Moreparticularly, there is a need for a braking system that reduces oreliminates the need for regular maintenance and replacement parts, canbe used over a relatively large range of rotor speeds, and minimizes theimpact of a braking procedure on other or adjacent wind turbinecomponents.

SUMMARY

According to one embodiment, a wind turbine generator includes an outerhousing, a drive shaft rotatably mounted within the outer housing, astator assembly positioned within the outer housing, and a rotorassembly positioned within the outer housing, wherein the statorassembly is coupled to the outer housing so as to be stationary and therotor assembly is operatively coupled to the drive shaft so as to berotated with rotation of the drive shaft. The generator may furtherinclude a heat exchanger for removing heat from the generator, and ablower positioned within the outer housing for generating a first fluidflow circuit within the generator configured to transport heat from atleast one of the stator and rotor assemblies to the heat exchanger. Theblower includes a first rotating plate. In accordance with an embodimentof the invention, a first eddy current brake is positioned within theouter housing and includes a first rotating member. The first rotatingmember of the first eddy current brake is positioned in the first fluidflow circuit established by the blower such that fluid moving in thefirst fluid flow circuit passes over the first rotating member so as tocool the first rotating member.

In an exemplary embodiment, the first eddy current brake is integratedwith the blower. More specifically, the first rotating plate of theblower operates as the first rotating member of the first eddy currentbrake. The first eddy current brake may include a first magnet assemblyincluding a plurality of electromagnetic modules positioned in closeproximity to the first rotating member, wherein the generator furtherincludes a controller for controlling the current to the electromagneticmodules so as to control the braking provided by the first eddy currentbrake.

The generator may include a second eddy current brake positioned withinthe outer housing and including a second rotating member, wherein thesecond rotating member is positioned in the first fluid flow circuitestablished by the blower such that fluid moving in the first fluid flowcircuit passes over the second rotating member so as to cool the secondrotating member. In an exemplary embodiment, the second eddy currentbrake is integrated with a blower. For example, the second eddy currentbrake may be integrated with the same blower that is integrated with thefirst eddy current brake. The blower may include a second rotatingplate, wherein the second rotating plate of the blower may operate asthe second rotating member of the second eddy current brake. The secondeddy current brake may include a second magnet assembly including aplurality of electromagnetic modules positioned in close proximity tothe second rotating member, wherein the generator may include acontroller for controlling the current to the electromagnetic modules soas to control the braking provided by the second eddy current brake.

The generator may include a second fluid flow circuit flowing throughthe heat exchanger configured to remove heat from the first fluid flowcircuit and transfer the heat away from the generator. In this regard,the heat exchanger may include a plurality of conduits extendingtherethrough configured to carry the fluid from the first fluid flowconduit and maintain the fluid of the first fluid flow circuit isolatedfrom the fluid of the second fluid flow circuit. In an exemplaryembodiment, the heat exchanger may include a water jacket. Moreover, therotor assembly rotating with the drive shaft may include a plurality ofpassageways extending along a length thereof configured to carry thefluid from the first fluid flow circuit.

In one embodiment, a wind turbine includes a tower, a nacelle disposedadjacent a top of the tower, a rotor including a hub and at least onewind turbine blade extending from the hub, and a generator disposed inthe nacelle. The generator includes an outer housing, a drive shaftrotatably mounted within the outer housing, a stator assembly positionedwithin the outer housing, and a rotor assembly positioned within theouter housing, wherein the stator assembly is coupled to the outerhousing so as to be stationary and the rotor assembly is operativelycoupled to the drive shaft so as to be rotated with rotation of thedrive shaft. The generator may further include a heat exchanger forremoving heat from the generator, and a blower positioned within theouter housing for generating a first fluid flow circuit within thegenerator configured to transport heat from at least one of the statorand rotor assemblies to the heat exchanger. The blower includes a firstrotating plate. A first eddy current brake is positioned within theouter housing and includes a first rotating member. The first rotatingmember of the first eddy current brake is positioned in the first fluidflow circuit established by the blower such that fluid moving in thefirst fluid flow circuit passes over the first rotating member so as tocool the first rotating member.

In a further embodiment, a method of operating a wind turbine generatorhaving an outer housing, a drive shaft rotatably mounted within theouter housing, a stator assembly positioned within the outer housing, arotor assembly positioned within the outer housing, and a heat exchangerincludes driving the drive shaft of the generator using a rotor of awind turbine; rotating the rotor assembly relative to the statorassembly to generate electricity; establishing within the outer housinga first fluid flow circuit configured to transport heat to the heatexchanger, the first fluid flow circuit being established by a blowerhaving a first rotating plate; positioning a first eddy current brakewithin the outer housing such that a first rotating member of the firsteddy current brake is positioned in the first fluid flow circuit; usingthe first eddy current brake to apply a braking force; and cooling thefirst rotating member by passing fluid moving in the first fluid flowcircuit over the first rotating member.

The method may further include integrating the first eddy current brakeinto the blower. More particularly, the method may include using thefirst rotating plate of the blower as the rotating member of the firsteddy current brake. Still further, the method may include providing asecond eddy current brake positioned in the outer housing and having asecond rotating member; positioning the second rotating member in thefirst fluid flow circuit; and cooling the second rotating member bypassing fluid moving in the first fluid flow circuit over the secondrotating member. The second eddy current brake may be integrated into ablower. The method may further include using a second fluid flow circuitto remove heat from the first fluid flow circuit and away from thegenerator.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate an embodiment of the inventionand, together with a general description of the invention given above,and the detailed description given below, serve to explain theinvention.

FIG. 1 is a partially torn away perspective view of a wind turbinehaving a generator in accordance with an embodiment of the invention;

FIG. 2 is a perspective view of a generator in accordance with anembodiment of the invention;

FIG. 3 is a partial cross-sectional view of the generator shown in FIG.2;

FIG. 3A is an enlarged view of the generator portion shown in FIG. 3;

FIG. 4 is a schematic diagram of a wind turbine generator in accordancewith an embodiment of the invention;

FIG. 5 is a partial perspective view of blower-brake assembly inaccordance with an embodiment of the invention;

FIG. 6 is a disassembled view of the blower-brake assembly shown in FIG.5;

FIG. 7 is a schematic diagram of a wind turbine generator in accordancewith another embodiment of the invention;

FIG. 8 is a schematic diagram of a wind turbine generator in accordancewith another embodiment of the invention;

FIG. 9 is a schematic diagram of a wind turbine generator in accordancewith another embodiment of the invention; and

FIG. 10 is a schematic diagram of a wind turbine generator in accordancewith another embodiment of the invention.

DETAILED DESCRIPTION

With reference to FIG. 1 and in accordance with an embodiment of theinvention, a wind turbine 10 includes a tower 12, a nacelle 14 disposedat the apex of the tower 12, and a rotor 16 operatively coupled to agenerator 18 housed inside the nacelle 14. In addition to the generator18, the nacelle 14 houses miscellaneous components required forconverting wind energy into electrical energy and various componentsneeded to operate, control, and optimize the performance of the windturbine 10. The tower 12 supports the load presented by the nacelle 14,the rotor 16, the generator 18 and other components of the wind turbine10 that are housed inside the nacelle 14. The tower 12 of the windturbine 10 also operates to elevate the nacelle 14 and rotor 16 to aheight above ground level or sea level, as may be the case, at whichfaster moving air currents of lower turbulence are typically found.

The rotor 16 of the wind turbine 10, which is represented as ahorizontal-axis wind turbine, serves as the prime mover for theelectromechanical system. Wind exceeding a minimum level will activatethe rotor 16 and cause rotation in a direction substantiallyperpendicular to the wind direction. The rotor 16 of wind turbine 10includes a central hub 20 and at least one blade 22 that projectsoutwardly from the central hub 20. In the representative embodiment, therotor 16 includes three blades 22 at locations circumferentiallydistributed thereabout, but the number may vary. The blades 22 areconfigured to interact with the passing air flow to produce lift thatcauses the central hub 20 to spin about a longitudinal axis 24. Thedesign and construction of the blades 22 are familiar to a person havingordinary skill in the art and will not be further described. Forexample, each of the blades 22 may be connected to the central hub 20through a pitch mechanism (not shown) that allows the blades to pitchunder control of a pitch controller.

The rotor 16 may be mounted on an end of a main drive shaft 26 thatextends into the nacelle 14 and is rotatably supported therein by a mainbearing assembly 28 coupled to the framework of the nacelle 14. The maindrive shaft 26 is operatively coupled to one or more gear stages, whichmay be in the form of a gear box 30, to produce a more suitablemechanical input to the generator 18 located in the nacelle 14. The gearbox 30 relies on various gear arrangements to provide speed and torqueconversions from the rotation of the rotor and main drive shaft 26 tothe rotation of a secondary drive shaft 32 (FIG. 2) that operates as aninput to the generator 18. By way of example, the gear box 30 maytransform the relatively low rotational speed of the main drive shaft 26(e.g., 5 to 25 revolutions per minute (rpm)) to a relatively highrotational speed (e.g., 3,000 rpm or higher) of the secondary driveshaft 32 which is mechanically coupled to the generator 18. Although thewind turbine 10 has been described as an indirect drive system, itshould be realized that the wind turbine may also be configured as adirect drive system and remain within the scope of the invention.

The wind turbine 10 may be included among a collection of similar windturbines belonging to a wind farm or wind park that serves as a powergenerating plant connected by transmission lines with a power grid, suchas a three-phase alternating current (AC) power grid. The power gridgenerally consists of a network of power stations, transmissioncircuits, and substations coupled by a network of transmission linesthat transmit the power to loads in the form of end users and othercustomers of electrical utilities. Under normal circumstances, theelectrical power is supplied from the generator 18 to the power grid asknown to a person having ordinary skill in the art.

In accordance with an aspect of the invention, a brake assembly, andmore specifically an eddy current brake, may be incorporated into thegenerator of the wind turbine. As will be discussed in more detailbelow, incorporating the eddy current brake into the generator mayprovide certain benefits not currently available. More particularly,locating the eddy current brake within the generator may improve coolingof the brake, and thus provide improved or enhanced braking capabilitiesfor the wind turbine. Furthermore, locating the eddy current brakewithin the generator may allow generator designers and manufacturers tocombine certain functions or components so as to reduce the number ofcomponents, assembly time, and overall costs. To this end and asdiscussed below, the eddy current brake may be integrated with a blowerused to cool the heat-producing components of the generator.

In this regard, and in reference to FIG. 2, generator 18 includes anouter housing 34 configured to contain and shield the various internalcomponents of the generator 18 and one or more supports 36 forsupporting the generator 18 and for securing the generator 18 to thenacelle 14, such as to a floor or support frame of the nacelle 14.Because the generator 18 is a rotating machine, the outer housing 34 maybe generally cylindrical in shape having a first front end 38, a secondrear end 40, and a side wall 42 extending therebetween. The cylindricalconfiguration of the outer housing 34 is merely exemplary, however, andother shapes and configurations are possible for the outer housing 34. Agenerator drive shaft 44 may be disposed within the outer housing 34 andconfigured to be rotatable relative to the outer housing 34 about acentral axis 46 defined thereby. In this regard, the drive shaft 44 maybe rotatably supported relative to the outer housing 34 by one or morebearing assemblies 48 (FIG. 3). As such bearing assemblies are generallywell known in the art, any further description thereof is not considerednecessary. A portion of the generator drive shaft 44 may extend from thefront end 38 of the outer housing 34 where it may be coupled to thesecondary drive shaft 32 on the output side of the gear box 30 via asuitable mechanical coupling 50, as is generally known in the art.Accordingly, the generator drive shaft 44 rotates with the rotation ofthe secondary drive shaft 32, which is driven by rotor 16.

The generator 18 includes a stator assembly 52 and a rotor assembly 54,both shown schematically in FIGS. 3 and 3A, concentrically disposedrelative to each other within the outer housing 34. In an exemplaryembodiment, the stator assembly 52 is generally fixed and stationarywhile the rotor assembly 54 is configured to rotate relative to thestator assembly 52. Thus, in the exemplary embodiment, the statorassembly 52 may be operatively coupled to the outer housing 34 or to aframe or support wall 56 of the outer housing 34, and the rotor assembly54 may be operatively coupled to the generator drive shaft 44, whereinthe stator assembly 52 is disposed radially outward of the rotorassembly 54. For example, the rotor assembly 54 may include a frame orsupport 58 which is coupled to the drive shaft 44 such that the rotorassembly 54 rotates with rotation of the drive shaft 44.

The stator assembly 52 generally includes a plurality of coils (shownschematically). As the coils, and in particular their construction andarrangement in the stator assembly 52 are generally known to those ofordinary skill in the art, no further discussion is deemed necessary inorder to understand the various aspects of the invention. The rotorassembly 54 generally includes a plurality of magnetic elements forgenerating a magnetic field which induces a current in the coils carriedby the stator assembly 52. In one embodiment, it is contemplated thatpermanent magnets may be carried by the rotor assembly 54. In anotherembodiment, however, it is contemplated that electromagnets may becarried by the rotor assembly 54. As the magnets, and in particulartheir construction and arrangement within the rotor assembly 54 aregenerally known to those of ordinary skill in the art, no furtherdiscussion is deemed necessary in order to understand the variousaspects of the invention. In any event, the stator assembly 52 and rotorassembly 54 of the generator 18 cooperate to convert the mechanicalenergy received from the wind turbine rotor 16 into electrical energy sothat the kinetic energy of the wind is harnessed for power generation.Specifically, the movement of the magnets of the rotor assembly 54 pastthe stationary coils of the stator assembly 54 induces an electricalcurrent in the coils according to the precepts of Faraday's Law.

In the example above, the rotor assembly 54 is described as being thefield source (i.e., exciting component) of the generator 18 and thestator assembly 52 is described as being the current source (i.e.,armature winding). In alternative embodiments, however, the rotorassembly 54 may comprise the current source and the stator assembly 52may comprise the field source. Moreover, those skilled in the art willappreciate generator arrangements where the stator assembly 52 isdisposed radially inward of the rotor assembly 54 rather thanvice-versa. Thus, aspects of the invention are not limited to that shownand described herein.

The generator 18 includes a heat exchanger 60 for removing heat producedby various components of the generator 18. In an exemplary embodiment,the heat exchanger 60 may include a water jacket 62 having wallsdefining a closed interior cavity 64 which is in fluid communicationwith a water source 66 for providing water to the jacket 62. Forexample, in one embodiment, the water jacket 62 may be generallypositioned within the outer housing 34 such that walls of the jacket 62may be formed by an outer housing wall 68 and the inner support wall 56to which the stator assembly 52 may be coupled. The water jacket 62further includes a rear end wall 70 extending between walls 68, 56 forclosing off the interior cavity 64 at the rear of the generator 18. Afront end wall (not shown) similarly extends between walls 68, 56 at thefront of the generator for closing off the interior cavity 64 at thatend. Thus, the interior cavity 64 of the water jacket 62 is fluidlyisolated from the interior of the generator 18 such that water remainsseparated from the electrical components of the generator 18 (such asthe coils and magnets of the stator and rotor assemblies 52, 54,respectively). While the term water jacket is used herein, it should berealized that the invention is not limited to the use of water as thecoolant for the heat exchanger 60. In this regard, other fluid coolantsmay be used with jacket 62 to transport heat away from generator 18.

The water jacket 62 includes one or more inlets 72 in fluidcommunication with the water source 66, such that water may flow fromthe water source 66 into the interior cavity 64 of the water jacket 62under pressure, for example, from a pump 74 operatively coupled to thewater source 66. Water flowing through the interior cavity 64 picks upheat being generated by the generator 18, such as by the stator androtor assemblies 52, 54, and transfers that heat away from the generator18. In this regard, the water jacket 62 includes one or more outlets(not shown) in communication with a fluid reservoir for collecting theheated water. A second heat exchanger, such as a radiator or the like,may be provided and associated with the outlet or reservoir for removingthe heat collected by the water flowing through water jacket 62. Forexample, the heat may be transferred to the surrounding environment. Inany event, the cooled water from the second heat exchanger may then bere-circulated by directing the water back toward the inlet 72 of thejacket 62. Thus, the water (or other coolant) flowing through the jacket62 represents a first fluid flow circuit 76 (FIG. 4) in which heat fromthe generator 18 is transferred to the water and subsequently rejectedto the environment 78, for example.

Heat exchanger 60 is able to transfer heat away from the generator 18 bya conduction mode of heat transfer. For example, heat generated by thestator assembly 52 may be transferred through the walls of the jacket 62and to the water flowing therethrough due to the proximity of the statorassembly 52 relative to the jacket 62. However, to increase theefficiency of the heat exchanger 60, as well as to facilitate heatremoval from the rotor assembly 54, which is more remote from the waterjacket 62, a second fluid flow circuit 80 may be established fortransferring heat from the heat generating components 82 of thegenerator 18 and to the water in the first fluid flow circuit 76 via aforced convection mode of heat transfer. In this regard, the secondfluid flow circuit 80 may include an air flow circuit established in theinterior of the generator 18, wherein air is moved over or through thestator assembly 52 and/or the rotor assembly 54, and/or other heatgenerating components to pick up heat therefrom. The air may then bedirected through the jacket 62 such that the heat in the air istransferred to the water flowing through the jacket 62, thereby coolingthe generator 18.

To this end, and to establish the air flow circuit 80 in the generator18, the rotor assembly 54 includes a plurality of passageways 84generally extending along the longitudinal length of the rotor assembly54. The number of passageways 84 and their size may vary depending onthe specific application and those of ordinary skill in the art willrecognize how to configure the passageways 84 to achieve sufficient heattransfer from the rotor assembly 54. In any event, each end 86 of thepassageways 84 may be in fluid communication with an open, interiorspace 88 of the generator 18 within the outer housing 34 at the frontand rear ends thereof (only rear shown in FIGS. 3 and 3A). In a similarmanner, the heat exchanger 60, and more particularly the water jacket62, may include a plurality of conduits 90 extending along thelongitudinal length of the water jacket 62 and through the interiorcavity 64 thereof. The number of conduits 90 and their size may varydepending on the specific application and those of ordinary skill in theart will recognize how to configure the conduits 90 to achievesufficient heat transfer from the air and to the water. The conduits 90are fluidly isolated from the water flowing in the interior cavity 64 ofthe jacket 62 so that there is no mixing of the water and air streams.The conduits 90 extend through the end walls 70 of the jacket 62 suchthat their ends 92 are open to the interior space 88 within the outerhousing 34 at the front and rear ends thereof (again only rear shown inFIG. 3). The interior space 88 at the front and rear ends of thegenerator 18 and the passageways 84 and conduits 90 define the air flowcircuit 80 within the generator 18.

FIG. 4 is a schematic of the generator 18 and the heat exchanger 60according to this embodiment. In this figure, the heat generatingcomponents 82 of the generator 18, such as the stator and rotorassemblies 52, 54, transfer their heat to the fluid in the second fluidflow circuit 80 (e.g., the air flow circuit). The heat in the secondfluid flow circuit 80 is then transferred to the first fluid flowcircuit 76 (e.g., the water flow circuit) in the heat exchanger 60. Heatmay also be transferred to the first fluid flow circuit 76 directly fromthe heat generating components 82. The heat in the first fluid flowcircuit 76 may then be transferred to the environment 78 or othersuitable heat sink. As will be discussed below, the heat exchanger 60 orheat removal capabilities of the generator 18 may be an important aspectof incorporating the eddy current brake within the generator 18.

To create an air flow circuit 80 through the heat exchanger 60, asdescribed above, the generator 18 includes a prime mover for causing theair to flow through the generator 18 and thereby establish air flowcircuit 80. In accordance with an aspect of the invention, generator 18includes a fan or blower 94 for generating a flow of air through thegenerator 18. In this regard and in reference to FIGS. 5 and 6, theblower 94 includes a generally circular, disc-shaped base plate 96having a generally planar inner surface 98 and a generally planar outersurface 100 connected by an outer side wall 102. The base plate 96 maybe configured as a generally solid plate member made from, for example,steel or other suitable metal or material. The base plate 96 includes acentral aperture 104 configured to receive the generator drive shaft 44therethrough when assembled (FIGS. 3 and 3A). In one embodiment, thebase plate 96 may include a collar 106 having a flange integrally formedwith or coupled to the base plate 96, and a tubular extension extendingaway from inner surface 98 toward the front end of the generator anddefining the central aperture 104. The base plate 96 is configured to befixedly secured to the drive shaft 44, such as at collar 106, such thatthe base plate 96 rotates with rotation of the drive shaft 44.

The blower 94 further includes a plurality of blades or vanes 112configured to increase the pressure of the air in the blower 94 and fordirecting the air flow toward a periphery 114 of the blower 94. In anexemplary embodiment, the vanes 112 may be configured as generallyarcuately-shaped rectangular plates having a first side edge 116 fixedlysecured to the inner surface 98 of the base plate 96, a second side edge118, an outer end edge 120 of the vanes 112 positioned adjacent the sidewall 102 of the base plate 96, and an inner end edge 122 positionedadjacent, but spaced from the central aperture 104. The vanes 112 may bemade of steel or other suitable metal or material and coupled to baseplate 96 by welding or other suitable process. Each of the inner endedges 122 of the vanes 112 may be positioned at a fixed radius from thecentral axis 46 and outboard of the collar 106. As illustrated in FIG.6, the blower 94 may further include a generally circular, disc-shapedcover plate 124 having an outer surface 126, an inner surface 128, andan outer side wall 130 extending therebetween. The cover plate 124 maybe configured as a generally solid plate member made from steel or othersuitable metal or material. The outer surface 126 of the cover plate 124may be coupled to the second side edge 118 of the vanes 112, such as bywelding or suitable fasteners. The cover plate 124 also includes acentral aperture 132 defining an inner side wall 134, which in anexemplary embodiment may be located at a terminating end of a lipdirected away from the inner surface 128 and toward the front end 38 ofthe generator 18. The central aperture 132 may be generally larger thanthe central aperture 104 through the base plate 96 or defined by collar106. In an exemplary embodiment, the inner side wall 134 of the coverplate 124 may be located so as to be adjacent the inner end edge 122 ofthe vanes 112 (FIGS. 3 and 3A). As illustrated in FIG. 3 and discussedin more detail below, the central aperture 132 in the cover plate 124operates as an opening 136 between the generator drive shaft 44 and theinner side wall 134 for drawing air from the generator interior space 88into the blower 94.

In operation, and as best illustrated in FIGS. 3 and 3A, rotation of thegenerator drive shaft 44, such as, for example, from secondary driveshaft 32 (and rotor 16), causes the blower 94, and more specifically,the base plate 96, vanes 112, and cover plate 124 to rotate about thecentral axis 46. This rotation causes air in the interior space 88 ofthe generator 18, such as at its rear end as shown in FIGS. 3 and 3A, tobe pulled into the blower 94 through the opening 136. The air traversesthe interstitial spaces between adjacent vanes 112 and is ejected fromthe blower 94 along its periphery 114. The high pressure air is ejectedinto a head space 138 in fluid communication with the ends 92 of theconduits 90 which extend through the water jacket 62. As described abovein reference to FIG. 4, the heat in the air is transferred to the waterflowing through the water jacket 62. The now cooled air, which is stillunder pressure from the blower 94, is directed out of the ends 92 of theconduits 90 at the front end of the generator 18 into an interior space88 in fluid communication with the ends 86 of the passageways 84extending through the rotor assembly 54. Residual spaces in thegenerator 18, such as through the stator assembly 52, may also provideadditional air flow passageways through or across the heat generatingcomponents 82. As the air traverses these passageways, heat istransferred from the heat generating components 82 to the air. The nowheated air exits the ends 86 of the passageways 84 at the rear end ofthe generator 18 and is again pulled into the blower 94 to complete andrepeat the air flow circuit 80.

As mentioned above, and in a further aspect of the invention, an eddycurrent brake is incorporated into the generator 18. More particularly,the eddy current brake may be positioned within the outer housing 34 ofthe generator 18. Even more specifically, in an exemplary embodiment,the eddy current brake may be integrated with the blower 94 used togenerate the air flow circuit 80 within the generator 18, as describedabove. The structure and operating principles of eddy current brakes aregenerally well understood and broadly include a rotating metal disc ormember located within a magnetic field generated, for example, bymagnets in proximity to the rotating member. The passing of the metalmember through the magnetic field creates eddy currents in the member.The eddy currents, in turn, generate an opposing magnetic field inaccordance to Lenz's law which opposes the rotation of the member. Thisopposing force effectively operates as a braking force for slowing therotation of the member. The net result is that the motion of therotating member is converted into heat in the rotating member. Thus, therotating member may become extremely hot depending on, for example, theamount of braking required. The magnets that generate the magnetic fieldmay be permanent magnets, but preferably include electromagnets. The useof electromagnets allows the current to the coils of the electromagnetsto be controlled, which in turn allows the strength of the magneticfield to be controlled. The strength of the eddy currents created withinthe rotating member is related to the strength of the magnetic fieldsuch that by controlling the current to the electromagnets, the brakingforce on the rotating member may be controlled.

FIGS. 3 and 3A, 5 and 6 illustrate an exemplary embodiment of an eddycurrent brake, generally shown at 150, incorporated within the generator18. The eddy current brake 150 includes a magnet assembly 152 and arotating member 154 in proximity to the magnet assembly 152. The magnetassembly 152 includes a generally circular, disc-shaped backer plate 156having a generally planar inner surface 158 and a generally planar outersurface 160 connected by an outer side wall 162 (FIG. 3). The backerplate 156 may be configured as a generally solid plate member made from,for example, steel or other suitable metal or material. The backer plate156 includes a central aperture 164 defining an inner side wall 166. Thebacker plate 156 may be configured to be coupled to the stationaryportions of the generator 18 such that it does not rotate with rotationof the drive shaft 44.

A plurality of electromagnetic modules 168 may be coupled to the innersurface 158 of the backer plate 156 and circumferentially spacedthereabout as shown in FIG. 6 such that substantially the entirecircumference of the backer plate 156 (e.g., adjacent the outer sidewall 162) includes an electromagnet module 168. The electromagneticmodules 168 may be configured as DC electromagnets. As the constructionand arrangement of the electromagnetic modules 168 are generally knownto those of ordinary skill in the art, no further discussion is deemednecessary in order to understand the various aspects of the invention.In any event, the electromagnetic modules 168 may be operatively coupledto a controller, schematically shown at 170, for controlling the currentsupplied to the modules 168, thus controlling the braking force on thegenerator drive shaft 44 as explained above (FIG. 3A).

As illustrated in FIGS. 3 and 3A, the magnet assembly 152 may be placedin close proximity to the blower 94. More particularly, the magnetassembly 152 may be located such that the electromagnetic modules 168are adjacent and generally confront the outer surface 100 of the baseplate 96 of the blower 94, such as being separated by a small air gap.In this way, and in one aspect of the invention, the base plate 96 ofthe blower 94 may be used as the rotating member 154 of the eddy currentbrake 150. Thus, in this embodiment, the blower 94 and the eddy currentbrake 150 are combined in a manner to provide an integrated blower-brakeassembly 172. In this context, integrated means that at least onecomponent of the blower 94 is used as a component of the eddy currentbrake 150. As noted above, in this embodiment, the base plate 96 of theblower 94 is used as the rotating disc or rotating member 154 of theeddy current brake 150. Thus, a more efficient use of existingcomponents is achieved.

In use, during normal operations of the wind turbine 10, no current issupplied to the electromagnetic modules 168, as dictated, for example,by controller 170. Consequently, the electromagnetic modules 168 do notgenerate an electric field and thus no braking force is applied to thebase plate 96 of the blower 94 (operating as the rotating member 154 ofthe eddy current brake 150). However, when it is desired to reduce therotational speed of the rotor 16 of the generator 18, such as duringhigh speed conditions, a grid fault, or at other over-speed conditions,the controller 170 may be configured to supply a current to theelectromagnetic modules 168. As noted above, this causes a braking forceto be applied to the base plate 96 of blower 94, and consequently to thedrive shaft 44 and ultimately to the rotor 16 through the wind turbinedrive train. Accordingly, the rotor 16 and generator drive shaft 44 arereduced in speed as a result of the braking. The amount of braking, andthus the amount of current supplied to the electromagnetic modules 168,may vary depending on the specific application and other factors. Thoseof ordinary skill in the art will recognize the amount of current tosupply to the electromagnetic modules 168 to achieve the desired brakingin the wind turbine 10.

As noted above, the braking operation causes the rotating member 154,which in this case is the base plate 96 of the blower 94, to heat up. Inanother aspect of the invention, integration of the blower 94 and theeddy current brake 150 may provide certain benefits. In this regard, thebase plate 96 is part of the air flow circuit 80 established within thegenerator 18. Thus, the moving air caused by the blower 94 flows overthe heated base plate 96 (e.g., as it traverses the interstitial spacebetween the vanes 112) and heat is transferred from the base plate 96 tothe air. This provides a cooling effect to the base plate 96. Of course,the heat transferred to the air from the base plate 96 may betransferred to the water flowing through the water jacket 62 asdescribed above. Thus, by integrating the eddy current brake 150 withthe blower 94, the heat exchanger 60 of the generator 18 may be used toextract heat therefrom. FIG. 4 schematically illustrates this exemplaryembodiment. In this regard, the overlap in the blower 94 and eddycurrent brake 150 (depicted by cross hatching) illustrates that the baseplate 96/rotating member 154 is shared between the two components. FIG.4 also illustrates that the shared component (base plate 96 of theblower 94/rotating member 154 of eddy current brake 150) is incorporatedwithin the air flow circuit 80 established within the generator 18 sothat the shared component is cooled by the air flow.

The ability to cool the rotating member 154 of the eddy current brake150 (e.g., the base plate 96) may provide certain advantages. Forexample, the amount of rotor or generator braking may be limited by theamount of heating permitted within the rotating member 154. For example,the temperature of the rotating member 154 may not exceed a maximumtemperature due to, for example, certain material or structuralrequirements. If the rotating member 154 is actively cooled, then theamount of braking provided by the eddy current brake may besignificantly increased. Thus, more aggressive braking may be applied.Additionally, in conventional eddy current brakes, the rotating memberis typically cooled by free convection, which in many cases issignificantly less efficient than forced convection. Thus, it may take arelatively long time for the rotating member to cool after being heatedby a braking operation. This may become problematic in situations wherebraking frequency may be high or the maximum temperature of the rotatingmember is reached. In the instant invention, using forced convention tocool the rotating member allows the rotating member to be cooled morequickly, thus making braking using the eddy current brake more readilyavailable, even in high frequency situations.

While the above describes an exemplary embodiment of the invention,there are a number of alternative embodiments that remain within thescope of the present invention. As described above, the integratedblower-brake assembly 172 includes a single rotating member 154 and asingle magnet assembly 152. However, additional rotating member/magnetassembly pairings may be included within the generator 18. By way ofexample and as illustrated in FIG. 7, the cover plate 124 of the blower94 may operate as a rotating member 154 for a second eddy current brakeon the inner side of the blower 94. In this regard, a second magnetassembly may be positioned in close proximity to the cover plate 124such that the electromagnetic modules carried thereby are adjacent andgenerally confront the inner surface 128 of the cover plate 124 of theblower 94. The electromagnetic modules on the second magnet assembly maybe coupled to the controller 170 so as to control the braking providedby this additional eddy current brake.

Similar to the above, a braking operation will cause the cover plate 124to heat up. However, similar to the base plate 96, the cover plate 124is part of the air flow circuit 80 established within the generator 18.Thus, the moving air caused by the blower 94 flows over the heated coverplate 124 (e.g., as it traverses the interstitial space between thevanes 112) and heat is transferred from the cover plate 124 to the air.This provides a cooling effect to the cover plate 124 and the heattransferred to the air from the cover plate 124 is transferred to thewater flowing through the water jacket 62 as described above. Those ofordinary skill in the art will recognize how to size the blower 94 suchthat a sufficient amount of cooling is provided in order to provide thedesired amount of braking to be performed by the eddy current brake(s)150.

In addition to a single or double eddy current brake 150 at the rear endof the generator 18, in another alternative embodiment, one or more eddycurrent brakes 150 may be provided at the front end of the generator 18.Since a blower is provided in the rear end of the generator 18, i.e.,blower 94, the eddy current brake at the front end of the generator 18may or may not be integrated within a blower. In those cases in which ablower is not provided, a rotating member 154 similar to the base plate96 may be provided (i.e., without the vanes 112 and cover plate 124). Amagnet assembly may be provided on one side of the rotating member(single eddy current brake) or on both sides of the rotating member(double eddy current brake). Additional rotating member/magnet assemblypairings may also be provided. When there is no blower at the front endof the generator 18, the eddy current brakes at that end of thegenerator 18 should be positioned such that air flowing along the airflow circuit 80 flows over the rotating member(s). Of course a blowermay also be provided at the front end of the generator 18 having asingle or multiple rotating member/magnet assembly pairings. Theseembodiments are schematically illustrated in FIGS. 8 and 9. In still afurther alternative, the blower-brake assembly 172 and its alternativesmay be provided only at the front end of the generator 18 (not shown).

In yet a further alternative embodiment, the blower 94 and the eddycurrent brake 150 may not be integrated (e.g., such that they no longershare a common component) but have a specific arrangement that may stillprovide certain benefits for locating the eddy current brake within thegenerator 18, and more specifically within the outer housing 34 thereof.In this regard, a benefit may still be gained if the eddy current brake150 is positioned within the air flow circuit 80 established by blower94 within the generator 18. Certainly making the base plate 96 (and/orcover plate 124) of the blower 94 operate as the rotating member 154 ofthe eddy current brake 150 allows the forced air to flow over the heatedrotating member to achieve cooling. The invention, however, is not solimited. Instead of sharing the base plate 96 of the blower 94, the eddycurrent brake 150 may include its own rotating member 154, formed by aplate member similar to the base plate 96 but not having the otherstructure of the blower attached thereto. The eddy current brake 150 maythen be positioned relative to the blower 94 within the generator 18such that the air flow generated by the blower 94 flows over theseparate rotating member 154. Thus, the invention is not limited to anintegrated blower-brake assembly 172. Instead, aspects of the inventionmay encompass an embodiment where the blower 94 and eddy current brake150 are separate, but the eddy current brake 150 is located within theair flow circuit 80 established by the blower 94 such that activecooling, e.g., that provided by forced connection, is achieved. Similarto above, one or more rotating member/magnet assembly pairings may beprovided. This alternative embodiment is schematically illustrated inFIG. 10, for example.

While the present invention has been illustrated by a description ofvarious preferred embodiments and while these embodiments have beendescribed in some detail, it is not the intention of the inventor torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. For example, the heat exchanger 60 isdescribed above as comprising the water jacket 62 within the outerhousing 34 of the generator 18. In alternative embodiments, however, theheat exchanger 60 may be positioned outside of the outer housing 34.Such arrangements are common in convention doubly-fed inductiongenerators, for example. The heat exchanger may be either an air-to-airor air-to-liquid heat exchanger. In addition to appreciatingmodifications like these, skilled persons will appreciate how thevarious features of the invention may be used alone or in anycombination depending on the needs and preferences of the user.

What is claimed is:
 1. A wind turbine generator, comprising: an outerhousing; a drive shaft rotatably mounted within the outer housing; astator assembly positioned within the outer housing; a rotor assemblypositioned within the outer housing, wherein the stator assembly iscoupled to the outer housing so as to be stationary and the rotorassembly is operatively coupled to the drive shaft so as to be rotatedwith rotation of the drive shaft; a heat exchanger for removing heatfrom the generator; a blower positioned within the outer housing, theblower generating a first fluid flow circuit within the generatorconfigured to transport heat from at least one of the stator and rotorassemblies to the heat exchanger, the blower including a first rotatingplate; and a first eddy current brake positioned within the outerhousing, the first eddy current brake including a first rotating member,wherein the first rotating member of the first eddy current brake ispositioned in the first fluid flow circuit established by the blowersuch that fluid moving in the first fluid flow circuit passes over thefirst rotating member so as to cool the first rotating member.
 2. Thewind turbine generator according to claim 1, wherein the first eddycurrent brake is integrated with the blower.
 3. The wind turbinegenerator according to claim 2, wherein the first rotating plate of theblower operates as the first rotating member of the first eddy currentbrake.
 4. The wind turbine generator according to claim 1, wherein thefirst eddy current brake further includes a first magnet assemblyincluding a plurality of electromagnetic modules positioned in closeproximity to the first rotating member, the generator further includinga controller for controlling the current to the electromagnetic modulesso as to control the braking provided by the first eddy current brake.5. The wind turbine generator according to claim 1, comprising a secondeddy current brake positioned within the outer housing, the second eddycurrent brake including a second rotating member, wherein the secondrotating member of the second eddy current brake is positioned in thefirst fluid flow circuit established by the blower such that fluidmoving in the first fluid flow circuit passes over the second rotatingmember so as to cool the second rotating member.
 6. The wind turbinegenerator according to claim 5, wherein the second eddy current brake isintegrated with a blower.
 7. The wind turbine generator according toclaim 5, wherein the first eddy current brake is integrated with theblower and, wherein the second eddy current brake is integrated with thesame blower that is integrated with the first eddy current brake
 8. Thewind turbine generator according to claim 7, wherein the blower includesa second rotating plate, the second rotating plate of the bloweroperating as the second rotating member of the second eddy currentbrake.
 9. The wind turbine generator according to claim 5, wherein thesecond eddy current brake further includes a second magnet assemblyincluding a plurality of electromagnetic modules positioned in closeproximity to the second rotating member, the generator further includinga controller for controlling the current to the electromagnetic modulesso as to control the braking provided by the second eddy current brake.10. The wind turbine generator according to claim 1, further comprisinga second fluid flow circuit, the second fluid flow circuit flowingthrough the heat exchanger and configured to remove heat from the firstfluid flow circuit and transfer the heat away from the generator. 11.The wind turbine generator according to claim 10, wherein the heatexchanger includes a plurality of conduits extending therethroughconfigured to carry the fluid from the first fluid flow circuit andmaintain the fluid of the first fluid flow circuit isolated from thefluid of the second fluid flow circuit.
 12. The wind turbine generatoraccording to claim 10, wherein the rotor assembly includes a pluralityof passageways extending along a length thereof configured to carry thefluid from the first fluid flow circuit.
 13. The wind turbine generatoraccording to claim 1, wherein the heat exchanger is configured as awater jacket.
 14. A wind turbine, comprising: a tower; a nacelledisposed adjacent a top of the tower; a rotor including a hub and atleast one wind turbine blade extending from the hub; and a generatordisposed in the nacelle, comprising: an outer housing; a drive shaftrotatably mounted within the outer housing; a stator assembly positionedwithin the outer housing; a rotor assembly positioned within the outerhousing, wherein the stator assembly is coupled to the outer housing soas to be stationary and the rotor assembly is operatively coupled to thedrive shaft so as to be rotated with rotation of the drive shaft; a heatexchanger for removing heat from the generator; a blower positionedwithin the outer housing, the blower generating a first fluid flowcircuit within the generator configured to transport heat from at leastone of the stator and rotor assemblies to the heat exchanger, the blowerincluding a first rotating plate; and a first eddy current brakepositioned within the outer housing, the first eddy current brakeincluding a first rotating member, wherein the first rotating member ofthe first eddy current brake is positioned in the first fluid flowcircuit established by the blower such that fluid moving in the firstfluid flow circuit passes over the first rotating member so as to coolthe first rotating member.
 15. A method of operating a wind turbinegenerator having an outer housing, a drive shaft rotatably mountedwithin the outer housing, a stator assembly positioned within the outerhousing, a rotor assembly positioned within the outer housing, and aheat exchanger, comprising: driving the drive shaft of the generatorusing a rotor of a wind turbine; rotating the rotor assembly relative tothe stator assembly to generate electricity; establishing within theouter housing a first fluid flow circuit configured to transport heat tothe heat exchanger, the first fluid flow circuit being established by ablower having a first rotating plate; positioning a first eddy currentbrake within the outer housing such that a first rotating member of thefirst eddy current brake is positioned in the first fluid flow circuit;using the first eddy current brake to apply a braking force; and coolingthe first rotating member by passing fluid moving in the first fluidflow circuit over the first rotating member.
 16. The method according toclaim 15, further comprising integrating the first eddy current brakeinto the blower.
 17. The method according to claim 16, furthercomprising using the first rotating plate of the blower as the rotatingmember of the first eddy current brake.
 18. The method according toclaim 15, further comprising: providing a second eddy current brakepositioned within the outer housing having a second rotating member; andpositioning the second rotating member in the first fluid flow circuit;and cooling the second rotating member by passing fluid moving in thefirst fluid flow circuit over the second rotating member.
 19. The methodaccording to claim 18, further comprising integrating the second eddycurrent brake into a blower.
 20. The method according to claim 15,further comprising using a second fluid flow circuit to remove heat fromthe first fluid flow circuit and away from the generator.